A mobile communication system controls switching a transmission diversity system for each channel, and improves the quality of the channel. When the channel type in an uplink is a channel for transmitting voice, open loop transmission diversity is used (steps S1→S3). When the channel type in an uplink is a channel for transmitting a packet, closed loop transmission diversity is used (steps S1→S2). Since the open loop transmission diversity or the closed loop transmission diversity whichever is more appropriate can be used, a transmission diversity system can be appropriately switched for each channel, thereby improving the quality of the channel.